Embodiments of the present invention relate to a method and process for the modification of membrane surfaces to significantly enhance the performance of filtration, separation, and remediation of a broad variety of chemicals, heavy metal ions, organic matters, and living organisms.
Generally speaking, issues related to bacterial infection and to the presence of heavy metals in water and wastewater systems have presented challenges for a long time and are still of a major concern today. The conventional ways to address bacterial issues include the use of chemicals (e.g. chlorinated compounds), UV treatment, heat treatment to treat or remove pathogens, and any combination thereof. In a similar manner, heavy metals are currently removed either using chelating agents (e.g. EDTA) or ion exchange processes that are specific to the metal of interest. Commercially used membrane filters have been applied for different purposes such as separation, cleaning, and protection. However, these filters cannot simultaneously remove heavy metals and inactivate microorganisms, which is a very important limitation to efficient water treatments.
Heavy metals released into the environment from metal plating, mining operations, metal finishing, welding, alloy manufacturing and agricultural activities pose a significant threat to the environment and public health due to their reported toxicity even at trace levels. Heavy metals are not biodegradable and tend to accumulate in living organisms, causing serious diseases and health disorders. Thus, effective removal of hazardous heavy metals from water and wastewater is very important and has become a challenging task for scientists and engineers. There are several available methods to treat or remove heavy metals; these include, but are not limited to, chemical precipitation, membrane filtration, ion exchange, adsorption and electrochemical technologies. Among these methods, adsorption is one of the most promising, and widely used methods due to its simplicity and low cost.
The popularity of heavy metal adsorption methods in wastewater treatment has resulted in the development of new adsorbent materials that can effectively remove heavy metals from solutions. Some of the adsorbents studied for adsorption of metal ions include activated carbon, fly ash, sawdust, crab shell, coconut shell, sugarcane bagasse, zeolite, rice husk, and iron and manganese oxides. However, these adsorbents have poor removal efficiencies for low concentrations of metal ions. The development of novel nanomaterials with increased affinity, adsorption capacity, and selectivity for heavy metals and other contaminants have recently gained more attention. Nanomaterials have become attractive as adsorbent materials because they have much larger surface areas than bulk particles. Moreover, some nanomaterials can be functionalized with various chemical groups to increase their affinity for target compounds. These unique properties of nanomaterials have been recently exploited by several researchers to develop high capacity and selective adsorbents for metal ions and anions.
Graphene-based polymer nanocomposites are one of the most promising and recent technological developments that combine unique features of graphene-based materials and polymer materials in one nanohybrid material. These nanohybrid materials show considerable improvement in properties that cannot normally be achieved using conventional composites or virgin polymers. Among the nanohybrid materials, polyvinyl-N-carbazole-graphene oxide (PVK-GO) nanocomposite is very promising, since it has different ways of polymerization, fabrication, and dispersion. Furthermore, PVK-GO has significant antimicrobial properties. However, no studies have, to date, explored the possibility of using PVK-GO to remove heavy metals.
Membrane separation systems are used for different sources of water with different water quality and have shown impressive promise for water treatment because of their potential to remove microorganisms and organic/inorganic pollutants. However, membrane operation and performance are often limited by a combination of phenomena, including but not limited to biofouling (e.g., bacterial adhesion), heavy metal contamination, and concentration polarization (i.e., solute build-up), particularly at the membrane surface. As such membrane biofouling is inherently complex, it is known to be initiated by the adhesion of one or more bacteria to the membrane surface, followed by the growth and multiplication of the sessile cells, which can eventually form a biofilm. Significant improvements in this art would involve new methods and processes that render membranes multifunctional, where such membranes would capture and separate all kinds of chemicals, including organic matters and living organisms, such as but not limited to bacteria.
Known technology in the field teaches the modification of the surface of commercial membranes using polymeric material incorporated with antibacterial silver agent. The present invention achieves improved results over existing systems by making use of carbon based nanomaterials, such as but not limited to graphene and graphene oxide (GO), which is known to possess significant anti bacterial properties, and by combining it with other agents such as but not limited to ethylenediamine tetraacetic acid (EDTA), which is known to be effective at removing heavy metals in solutions.
The choice of graphene, graphene oxide, or related variations is judicious because these materials not only possess anti-bacterial properties, but also improve membrane strength, thermal stability, and water flux. However, use of these nanomaterials (graphene, GO) as coating material on membranes has been limited due to its poor dispersion in most media and its high cost.
The approaches described in this section could be pursued, but are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section